Belief in conspiracy theories is not unique to Republicans -- 56 percent of Democrats believe in one of the four popular myths researchers asked about -- but it is more common. Among registered GOPers, 75 percent said at least one of the four theories was likely true. Moreover, researchers noted: "Generally, the more people know about current events, the less likely they are to believe in conspiracy theories -- but not among Republicans, where more knowledge leads to greater belief in political conspiracies."

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“There are several possible explanations for this,” said Fairleigh Dickinson political scientist Dan Cassino, who helped conduct the poll. “It could be that more conspiracy-minded Republicans seek out more information, or that the information some Republicans seek out just tends to reinforce these myths.”

The four theories they asked about were: birtherism (36 percent of all Americans believe it); that the government knew about 9/11 in advance (25 percent of Americans think that's probably true); that Obama stole the 2012 election (19 percent believe this one); and that George W. Bush stole the 2004 election via vote rigging (23 percent believe it).

Not surprisingly, Republicans are more likely to believe that Obama stole the 2012 election, while Democrats are more likely to think the same about 2004. Thirty-seven percent of Democrats think Bush or his supporters engaged in significant voter fraud to win that year, compared to just 9 percent of Republicans and 17 percent of independents.

9/11 conspiracy theories were also more popular among Democrats, with 36 percent believing that Bush knew the towers would be attacked, while young African-Americans are particularly likely to believe this myth -- fully 59 percent believe it.

But the most popular conspiracy theory of all was birtherism. “This conspiracy theory is much more widely believed mostly because it’s been discussed so often,” explained Cassino. “People tend to believe that where there’s smoke, there’s fire – so the more smoke they see, the more likely they are to believe that something is going on.”